1. Field of the Invention
The present invention relates generally to antenna arrangements and systems in the field of signal identification, such as radio frequency identification (RF/ID) technology and, in particular, to an antenna arrangement and system for use in connection with enclosures manufactured from field-absorbing or field-reflecting materials, such as metals, semi-metals, etc., the enclosure having one or more signal “null” regions therein.
2. Description of the Related Art
Radio frequency identification (RF/ID) technology is used in many applications for both communication and identification of objects, items, inventory and the like. For example, in many inventory applications, one or more objects that a user is desirous of tracking are “tagged” or otherwise identifiable by some identification component. When using RF/ID, the tag is energized, activated or activatable, such that it emits a signal that is uniquely indicative of its identification, contents or grouping.
In order to transmit and receive signals from the tag, an antenna is typically used. The antenna can energize the tag or otherwise communicate with the tag in order to gather the appropriate identity of the object. Such systems are often used for tracking many different and varying objects or items having unique identifications or tags in operable communication with a specific object or item. In addition, it is typical that the objects or items are stored in an enclosure, such as a cabinet, a storage bin, a specified room or area or other designated and bounded area.
When using RF/ID technology, it is often preferable to maximize or enhance the radio frequency signals emanating from the antenna and the tags. Further, since the objects are located in the enclosure, it is further preferable to minimize or eliminate the radio frequency signals emanating from the enclosure, which could interfere with the operation of other RF/ID systems located adjacent or near each other. Such fields could also interfere with the operation of different pieces of equipment, such as hospital machines and equipment.
Therefore, in order to minimize and typically eliminate the undesired field emanation, the enclosure is constructed from field-absorbing materials or field-reflecting materials, such as metallic or semi-metallic materials. Using these field-absorbing or field-reflecting materials leads to other drawbacks. The main drawback of using such materials is that, due to the nature of the antenna placement and the enclosure materials of construction, one and typically multiple signal “null” or “void” regions are created by the absorption.
According to the prior art, and as illustrated in FIG. 1, a typical antenna arrangement according to the prior art may include an antenna loop element 10 having a perimeter portion 12 positioned in an enclosure 14. The perimeter portion 12 of the antenna loop element 10 is located adjacent or near a corresponding perimeter area 16 of the enclosure. The antenna loop element 10 is in communication with a feed point mechanism 18 for transmitting and receiving signals to and from the antenna loop element 10. Since the enclosure 14 is constructed from a field-absorbing material, the resulting field is non-existent in certain enclosure 14 areas, referred to signal “null” regions 20. Therefore, if an object or item (and its corresponding RF/ID tag) is located in the signal “null” region 20, the antenna arrangement and system will not “read” or identify the object. This represents a fundamental failure in the system and represents a critical error in providing an accurate inventory system.